Gaps between window frame and wall

[Essex]

The SPAB website suggests lime mortar, a filler of rolled wet newspaper and a mastic from a fillet of sand and boiled linseed oil.
Any one any experience of this?

 

[skier-hughes]

Linseed oil and sand I've used. I filled one largish gap with lime mortar and tehn did the outsides with oil/sand. I've yet to do the insides.
Outisde has now been there about 3 months and looks the same as when it went in.

Graham

 

[Essex]

Much appreciated.
What sort of sand and what proportions?

 

[skier-hughes]

3.1 sand to oil.
I used the yellow builders sand that I had to make up the lime mortar for repointing. Not too coarse adn not too smooth. Seemed ideal.

Graham

 

[Nemesis]

Biff makes and uses it for windows. I think you can buy the mastic ready made too.

 

[Gervase]

Mike Wye sells it readymade, but it's cheaper to make your own.
Use the finest sand you can get - I seive soft building sand - and make sure it's bone dry. To make sure, put it in a Pyrex dish and give it an hour in a slow oven to get rid of any water. Cool and stir into linseed oil to make a thick mastic paste. It's sticky stuff, but it works a treat.

 

[biffvernon]

I think that the 'burnt' in 'burnt sand mastic' refers to the oven drying of the fine sand before adding the linseed oil. If you are just wanting a smallish quantity, putting the sand in a microwave is a very fast way of drying it out. The variety sold by Womersleys has some rosin in it - probably makes it set quicker.

 

[Essex]

Thanks, much appreciated

 

[tony]

I would like to try this on the gaps around my new window instead of the dow corning sealant thats waiting to be used.

How long does it take dry? weeks, months etc

I know its a proven method, but does it remain flexible or does it completely harden?

What sort of working time do you have with it.
Best Regards

Tony

 

[biffvernon]

Yes it sets in weeks or months and you have days of working time. Probably eventually goes as hard as the wood.

 

[Andrew Bodenham]

I've got a new window to seal in, so this thread is very interesting.

If sand/oil mastic goes off hard (eventually) how does it cope with the inevitable movement of a wood window frame due to moisture change & thermal movement? Don't you just end up with capillary cracks around the frame which then let in the weather? Or am I missing something?

 

[Gervase]

It doesn't seem to set rigid hard; the surface loses its tackiness after a couple of weeks, but the mastic itself seems to retain some elasticity, as it sticks to both the mortar and the woodwork without opening cracks, whatever the weather.

 

[biffvernon]

Wood is hard. Try hitting your head with a piece.
Wood is soft. Try digging you fingernail into a piece.
Linseed oil polymerises to form a hard but plastic material that sticks rather firmly to both the wood and the surrounding wall. It can accommodate small slow movements without cracking.

 

[Penners]

Use the finest sand you can get - I seive soft building sand - and make sure it's bone dry. To make sure, put it in a Pyrex dish and give it an hour in a slow oven to get rid of any water.

You can buy ready kilned sand - mainly used for grouting in concrete paving blocks. Would that be suitable, Biff?

 

[Bry]

Which linseed oil do you use, boiled or raw?

 

[Penners]

Wood is hard. Try hitting your head with a piece.
Wood is soft. Try digging you fingernail into a piece.

Or, if you're pressed for time, just dig your fingernail into your head.

 

[Craig]

I found the decision to use mastic an easy one:

The silicone sealant around my bath seems to last a year or two.
The mastic mortar around my windows seems to have lasted a century or two.

Mastic is a kind of plant resin, I believe. As noted, probably a drying agent.

 

[Penners]

The mastic mortar around my windows seems to have lasted a century or two.

Do you have any indication of what the mix of that mastic mortar is?

 

[Craig]

Dont know I am afraid - it may not be as old as I think but given the lack of maintenance everywhere else, I doubt its modern.

 

[biffvernon]

You can buy ready kilned sand

Some folk have just got too much money to spend.

Which linseed oil do you use, boiled or raw?

I don't suppose it makes very much difference. The boiled might set a bit faster.